Yes, pulling the hose off is a good way to give the system a "shock".. the rush of coolant drags out any bits of silt, loose limescale and rust particles so it's a good tip.
Similarly once you have refilled with the clean water, let the engine run a bit with the heater dial set to MAX (you don't need the fan on) so that the water can pass through the heater matrix and purge that too.
Bear in mind that coolant is the most toxic stuff on your car. When you first "dump" the coolant, catch it in an old washing up bowl and later on dispose of it down at your local Household Waste centre. Don't let it run down the drive and into the drains. It'll end up killing all manner of creatures and people.
There must be a way to grab a hold of the bleed screw. In the past (not on 500's though) I've removed lights and shifted the coolant reservoir etc, to make space. Last diesel I touched was a mate's Corsa and that was a bumper-off job.
Othewise the systems are quite good at bleeding themselves, if you can't easily access the little bleeder, then fill it as usual, squeeze the hoses as you go and try to flush as much air out as possible that way. When you're done, run the engine a bit and see if any remaining air in the rad' is carried out by the coolant just circulating normally. The level will probably drop and you'll have to top it up a couple of times until it stabilises.
Then if the radiatore gets hot all the way to the top and the level doesn't change any more, it's probably quite well bled and you can use it like that. If the rad' is cold at the top and hot at the bottom then it needs more bleeding. I dunno if you can reach the tap from below (long arms) maybe...
Ralf S.
